At noontime, most of the light reaching our eyes appears blue due to gases in our atmosphere scattering it more widely than violet and red hues do.
Reason being, air molecules are smaller than the wavelengths of sunlight and shorter wavelengths scatter more strongly compared to longer ones – known as Rayleigh scattering effect.
The Sun
As sunlight travels through Earth’s atmosphere, it becomes scattered by gases and particles in the air, most significantly shorter wavelengths such as blue and violet light which tend to interact more strongly with molecules found within our atmosphere such as nitrogen and oxygen molecules. This phenomenon can be particularly prominent at shorter wavelengths like blue and violet which tend to collide more often with molecules present such as nitrogen and oxygen molecules in our environment.
Longer wavelength light such as red and orange wavelengths tend to reach our eyes more directly and are thus less scattered, creating white skies during the daytime. At sunrise and sunset however, our atmosphere obstructs less of this longer-wavelength red-orange light reaching us allowing it to give rise to striking hues of orange-red in our skies.
Mars also boasts a thin atmosphere made up of carbon dioxide, similar to Earth. When sunlight passes through this atmosphere it has an orange tint due to carbon dioxide reddening it during sunset, making the Sun appear even more orange than on Earth.
As we gaze upon the sky, our eyes see an amalgam of colors from across the spectrum; blue is dominant due to Rayleigh scattering and is therefore why the sky appears predominantly blue instead of purple. Although its hue may change depending on various circumstances – for instance, pollution in the air might make the sky seem more gray while clear skies make the sky seem bluer due to less dust particles scattering sunlight – one way or the other, your view remains the same!
Atmosphere
The color of the sky depends on how light is scattered by Earth’s atmosphere, making its hue distinct at various times and locations. When light enters Earth’s atmosphere it hits dust particles, smoke and water vapor that scatter it across its entirety; when this happens certain wavelengths (blue/violet light waves being shorter than others in visible spectrum) scatter more widely, giving an uneven sky that makes white appear like its center color.
Researchers refer to this process as Rayleigh scattering, after the British physicist who first proposed this theory in 1871.
Visible light acts like both a wave and particle; its vibratory frequency determines its color perception while wavelength (the measure of distance as opposed to time; further away things are, the smaller their wavelength will be).
As visible light travels through Earth’s atmosphere, it collides with air molecules–in particular nitrogen and oxygen molecules–that scatter it more. Since oxygen and nitrogen particles are much smaller than light wavelengths, more light of longer wavelengths like red and yellow is not scattered as much compared with blue or violet lights, which scatter up to 10 times more.
As a result, we perceive the sky as blue. Because sunlight interacts with particles in the atmosphere more directly at sunrise and sunset, the skies can appear different at those times of day; weather, terrain features and human activities (such as CO2) all play roles in altering its composition and hence how we perceive the sky in different locations.
Clouds
Visible light acts like a wave (and also as particles; that’s another story). Each wavelength has a particular length; from red being longest to violet having shorter ones. As wavelengths interact with various substances they reflect or absorb light differently – giving each color its distinct look. When sunlight passes through our atmosphere it scatters more blue wavelengths than red wavelengths; hence why our sky appears blue, not violet or yellow!
Nitrogen and oxygen molecules in the air primarily participate in scattering by their size; longer wavelengths (red and orange) pass through more easily while shorter ones (blue and violet) get scattered more strongly, and our eyes perceive this scattering as the sky’s blue hue.
As the Sun moves lower in the sky during sunset and sunrise, more atmospheric particles get in its path, scattering blue light away and redirecting it toward the horizon to give an orangey tint to its image.
Clouds also play a part in making the sky blue. Water vapour in the air, mixed with salt and dust particles, condenses into visible droplets of water called condensation nuclei that collide with sunlight to produce blue wavelengths that we perceive as part of its color palette. When they hit its surface and absorb some of its energy they emit this hue as part of what gives our skies their signature blue hue.
Other factors can also impact the color of the sky, such as weather and local terrain (dust), pollution levels (CO2) and human activity (CO2). But for the most part, blue sky prevails.
The same processes that give the sky its blue hue also explain why open water, whether a lake or ocean, appears blue. Water molecules reflect blue light while absorbing longer red and orange wavelengths to produce this effect; were it completely clear, it would appear pure white instead.
Latitude
What gives the sky its vibrant hue is how its interaction with different particles and gases in Earth’s atmosphere. Sunlight passes through, scattering off of atmosphere particles with shorter wavelengths (blue/violet light is most susceptible), known as Rayleigh scattering; this phenomenon accounts for why our sky appears bluer; longer wavelengths such as red/orange tend not to scatter off as easily so more of their light makes its way directly through to our eyes.
When the Sun rises above the horizon, its light has to travel through more atmosphere, giving its rays more chances for dispersion – hence why skies look less blue nearer its zenith. Furthermore, sunsets often look reddish because blue light gets scattered away while only reddish light reaches our eyes.
Humidity and pollution levels also influence the color of the sky, meaning its hue may shift depending on where you are. Countries such as Singapore, India or Australia with humid air tend to have skies with more or less blue hues while countries like Canada, US or Russia with dry atmospheres tend to feature bluer skies.
Rayleigh scattering may explain why Mars, with its thin atmosphere of carbon dioxide and dust particles, displays such vivid blue skies. There’s a good chance this process could also account for sky colors on other planets; unfortunately we lack evidence for this claim yet.
Astronomical latitude refers to an angle measured from any point on Earth perpendicular to the Equator, creating one half of a great circle. Longitude measures distance north or south from any given point along Greenwich Meridian in London. Since latitude lines parallel longitude lines, their distance decreases closer to either pole. When drawing parallel lines across a globe this phenomenon causes them to get thinner closer towards its center.